1. Field of the Invention
The present invention relates to a semiconductor device and a producing method of the same.
2. Description of the Prior Art
A conventional producing method of a flash memory is as follows. First, an active region is formed on a silicon substrate. A first oxide film (film thickness is about 100 Å) is formed on the active region. A first polysilicon film (film thickness is about 1000 Å) is formed on the first oxide film by CVD (Chemical Vapor Deposition) method. A second oxide film is formed on the first polysilicon film, and a second polysilicon film is formed on the second oxide film.
Finally, the first polysilicon film becomes a floating gate of a flash memory cell, and the second polysilicon film becomes a control gate. The first oxide film electrically insulates between the active region and the floating gate (first polysilicon film), and the second oxide film electrically insulates between the floating gate (first polysilicon film) and the control gate (second polysilicon film).
On the second polysilicon film, a tungsten silicide film is formed which functions as an electrode.
Next, photolithography process and etching process are carried out to form a flash memory cell having desired characteristics. Then, a third oxide film for covering the flash memory cell is formed. Then, a flash memory is completed through some processes.
According to the conventional producing method, however, in the etching process for forming a gate electrode of the flash memory cell, and in an ion implantation process for forming the active region, there is an adverse possibility that a gate oxide film (first oxide film/second oxide film) constituting the flash memory cell is damaged.
If the gate oxide film is damaged and a film quality is deteriorated, the insulation performance between the floating gate (first polysilicon film) and the active region is deteriorated, and the insulation performance between the floating gate and the memory cell electrode is also deteriorated. As a result, there is a possibility that data retention time and the number of data rewriting which are required for the flash memory cell can not be secured.